Generally, a so called HST (Hydro Static Transmission) is mounted in some work vehicles such as wheel loaders, or the like. In an HST type work vehicle, a hydraulic pump is driven by an engine, and the hydraulic pressure motor for travel is driven by the hydraulic oil ejected by the hydraulic pump. Because of this, the work vehicle travels. In an HST type work vehicle of this kind, by controlling the engine rotational speed, the displacement of the hydraulic pump, and the displacement of the hydraulic motor for travel, and the like, it is possible to control the vehicle speed and the traction force. For example, in Japan Patent Laid-open Patent Publication JP-A-2010-223416 has been disclosed a work vehicle that can aim to reduce the fuel consumption by discriminating the working conditions, and the like, and varying the absorption torque of the hydraulic pump. In this work vehicle, the control mode of the hydraulic pump is switched between the high power mode and the low fuel consumption mode according to the working conditions. When the control mode is switched from the high power mode to the low fuel consumption mode, the matching point of the absorption torque curve of the hydraulic pump with respect to the output torque curve of the engine is changed from the high rotational speed side to the low rotational speed side. At this time, for example, as is shown in FIG. 5, the absorption torque curve of the hydraulic pump is changed from the absorption torque curve of the high power mode to the absorption torque curve of the low fuel consumption mode. Because of this, the matching point is changed from the point MA1 on the high rotational speed side to the point MB1 on the low rotational speed side.